1. Field of the Invention
The present invention generally relates to a motor for electric pumps that forcefully feeds oil or other fluids. More particularly, the present invention relates to a motor for electric pumps that forcefully feeds oil or other fluids by driving a piston pump and a method of balancing motor rotation.
2. Related Art
In a conventional motor for electric pumps that drives a piston pump in order to forcefully feed oil or other fluids, as illustrated in FIG. 6, armature shaft 107 forms the spindle of the motor for electric pumps and is provided with eccentric portion 108 for driving piston pump 104. Alternatively, a conventional motor for electric pumps may employ an eccentric cam (not illustrated) instead of eccentric portion 108 of armature shaft 107. In either case, armature shaft 107 is unbalanced due to eccentric portion 108 or the eccentric cam, and as a result, the smooth rotation thereof is impeded.
To solve the above problem, a rotor of motors for electric piston pumps is disclosed in Japanese Unexamined Patent Publication No. 4-248345. In this publication, a first balance weight and a second balance weight are mounted on the armature shaft at both sides of the core in order to offset the eccentricity caused by the eccentric portion of the armature shaft for driving the piston pump.
Nevertheless, in motor 100 for electric pumps composed as above, parts forming first and second balance weights 105 and 106 are essential for achieving the smooth rotation of the armature shaft 107. A production process for mounting the above parts on armature shaft 107 is also required. These requirements not only bother the improvement of the productivity of motor 100 for electric pumps but also cause an increase in the production cost.
In addition, as the balance weights 105 and 106 are mounted on armature 102 at both sides of the core, another problem exists; the size and shape of the balance weights are restricted.